Cross-flow fluid machines



April 8, 1969 B. ECK ET Al.

CROSS-FLOW FLUID MACHINES Sheet Original Filed Sept. 5, 1962 INVENTORSBRUNO ECK NIKO US LAING ATTORNEYS April 8, 1969 B. ECK ET AL. 3,437,262CROSS-FLOW FLUID MACHINES Original Filed Sept. 5, 1962 Sheet Z of 2INVENTORS BRUNO ECK NIKOLAUS LAING av y w, 2104., 4%,!

a ATTORNEYS United States Patent US. Cl. 230-114 6 Claims ABSTRACT OFTHE DISCLOSURE A cross flow fluid machine having an auxiliary guide bodyin the discharge region of the machine to assist in positioning andstabilizing a fluid vortex within the machine.

This invention relates to cross-flow fluid machines for inducingmovement of fluids which is to be understood as including both liquidsand gases, and this application is a division of application Ser. No.453,458 filed May 5, 1965, now Patent No. 3,249,292, itself a divisionof application 221,620 filed Sept. 5, 1962, now abandoned, which in turnis a continuation-in-part of application Ser. No. 671,114, filed July 5,1957 and now abandoned. The invention relates more particularly tocross-flow machines of the type comprising a hollow cylindrical bladedrotor mounted for rotation about its axis and through which, inoperation of the machine, fluid passes at least twice through the pathof the rotating blades in a direction transverse to the axis of therotor.

The invention concerns more especially fluid flow machines for operationunder conditions of low Reynolds numbers. The Reynolds number of aparticular fluid flow condition is a dimensionless number representingthe ratio of the product of flow velocity and a characteristic lineardimension of the part under observation to the kinematic viscosity ofthe fluid. For the purpose of the present appilcation Reynolds number(Re) will be defined as where d is the blade depth radially of therotor, c is the peripheral speed of the rotor, and 'y is the kinematicviscosity of the fluid, the latter being equal to the quotient of thedynamic viscosity and density. A Reynolds number is considered herein tobe low if, as above defined, it is less than X 10 From the definitionjust given, it will be understood that the invention concerns moreespecially flow machines which are small dimensionally, run at lowperipheral speeds, or are intended for use with air or other gas havinga low density or used with a fluid having a high viscosity.

It is known that in a flow machine having bladed rotors, an initialacceleration and a subsequent deceleration of the flow occurs inboundary layers on the suction side of each blade as fluid passes overthe blade. The higher the viscosity of the fluid in relation to itsdensity or in relation to the relative velocity between the blade andfluid (i.e. the lower the Reynolds number) the greater is thedeceleration of the boundary layer in the deceleration zone of theblade. If the boundary layer is slowed down suificiently it separatesfrom the blade and no longer follows the blade contour. The point atwhich separation occurs is known as the separation point. The separationpoint travels forward along the surface of the blade against thedirection of flow in proportion to the increase in the eifect of theviscosity relative to density or to the decrease in the relativevelocity between the fluid and the blade.

The movement forward of the separation point along the blade because oflow Reynolds number conditions produces a number of undesirable effectsin the type of flow machine described. A vorticity zone in which thekinetic energy of the fluid is converted into thermal energy is producedafter the separation point with the result that the efliciency of themachine drops. The degree of deflection of the fluid in passing throughthe path of the rotating blades decreases owing to the fact that theflow does not follow the full extent of the blade profile. This resultsin less pressure gain in the machine since pressure gain is determinedby the extent of the deflec tion of the stream tubes in the bladechannel. Finally, the turbulent flow in back of the separation pointeffectively reduces a part of the cross-section of the blade channels sothat the throughput through the rotor of the machine also diminishes.

For the reasons given, it has previously been considered that theoperation of flow machines under conditions of low Reynolds numberswould necessarily and inesca ably involve low efliciencies in comparisonwith efliciences obtainable under conditions of high Reynolds numbers.For example, although the inefliciency of the small blowers abovereferred to has been notorious, it has been tolerated simply because ithas not hitherto been thought capable of improvement.

It has hitherto been thought that to avoid mixing losses a flow machineshould always be designed to have a rectangular velocity profile atevery section taken across the flow, that is, the graph of velocity offluid flow at a given point plotted across the flow channel should riserapidly from zero at one side of the channel to a steady valuemaintained over the greater part of the section and should then dropagain rapidly to zero at the other side. It has also been assumedhitherto that a flow machine of the type described should always havethe blades loaded approximately equally by the fluid in the circumferential zones where the fluid passes through the rotor blades. Thesetwo related conditions can normally be satisfied without muchdifliculty.

Following the principles hitherto generally adhered to in the art andenunciated above, one skilled in the art would normally prefer to designa cross-flow type blower, such as that shown in Patent No. 2,742,733, soas to work under conditions of high Reynolds numbers and would designthe blade angles and ducting on the basis of, and with a view toproducing a rectangular velocity profile throughout the blower and anequal loading on the rotor blades in the circumferential zones where thefluid passes these rotor blades. On the other hand, if operation at lowReynolds numbers could not be avoided, the same design principles wouldnormally be applied and the resulting lower efliciency regarded asinevitable.

An object of the present invention is to provide a cross-flow machinecapable of operating under conditions of low Reynolds numbers withbetter efliciency than has hitherto been regarded as acceptable.

The invention depends in part on the appreciation that contrary to whatas previously been thought by those skilled in the art, it can beadvantageous under flow conditions of low Reynolds numbers to bringabout in a flow machinery a velocity profile having a pronounced maximumwith a consequent very unequal loading of the blades in thecircumferential zones through which fluid passes. This velocity profilewith a pronounced maximum gives rise to some flow tubes within theblower having much greater velocity than the other flow tubes within theblower.

In the restricted circumferential zones of the rotor blades throughwhich the high velocity stream tubes pass, correspondingly high relativevelocities exist locally between the fluid and the blades, so that inthese zones momentum is imparted to the fluid at efliciencies whichcould otherwise be obtained only with machines operating underconditions of correspondingly much higher Reynolds numbers. The velocityprofile with a pronounced maximum leads to lower velocities than themean velocity in other circumferential zones of the rotor blades and inthese zones transfer of momentum occurs at an efficiency which is lowerthan it would have been had the velocity profile been rectangular.However, the available momentum in a stream tube issuing from the bladesincreases with the square of its velocity; thus the momentum of thefluid as a whole is substantially concentrated in the high velocitystream tubes so that the transfer efliciencies in the zones of slowthroughflow have little eflect on the overall efficiency.

The invention depends in part also on the appreciation that theabove-mentioned velocity profile with a pronounced maximum can beobtained by setting up in the machine a cylindrical vortex including afield region with a velocity profile approximately that of a Rankinevortex and a core region eccentric to the rotor axis. A further objectof the invention therefore is to provide various means for forming andstabilizing the vortex.

Broadly, a cross-flow machine constructed according to the inventioncomprises a hollow cylindrically bladed rotor mounted for rotation aboutits axis and having its interior clear of stationary guides and with theblades of the rotor being curved with their outer edges leading theirinner edges. End wall means substantially aligned with the ends of thetrotor may be provided, the ends of the rotor being substantially closed.First and second guide walls may also be provided extending between theend walls over the length of the rotor and defining therewith an entryregion and a discharge region said rotor and guide walls co-operating onrotation of the rotor to set up and stabilize a fluide vortex having acore region extending lengthwise of the axis and eccentric theretoadjacent the first guide wall and guiding a fluid throughput through therotor from the entry region through the path of the rotating blades ofthe rotor to the interior thereof and thence again through the path ofthe rotating blades to the discharge region.

The invention includes also a body in said discharge region extendingparallel to the rotor axis between the end walls and spaced from theguide walls for flow of fluid to either side of said body. This body mayalfect the position or intensity of the vortex to produce a desiredeflect on the operation of the machine.

Referring to the drawings in which several embodiments of the inventionare illustrated:

FIGURE 1 is a cross-sectional view of a fluid flow machine constructedaccording to the invention;

FIGURE 2 is a graph illustrating velocity of fluid flow at the outlet ofa cross-flow fluid machine constructed according to the invention;

FIGURE 3 is a graph illustrating velocity of fluid flow at the outlet ofconventional cross-flow machines;

FIGURE 4 is a graph illustrating velocity of fluid flow within the fieldof a Rankine type fluid vortex;

FIGURE 5 illustrates the ideal fluid flow lines occurring in one halfthe cross-sectional area of a rotor of a machine of the type shown inFIGURE 1;

FIGURE 6 is a vector diagram illustrating flow of fluid contacting ablade on its second transversal of the path of the rotating blades orwhen the fluid passes from the interior of the rotor to the pressureside of the machine; and

FIGURE 7 is a cross-sectional view of a machine somewhat similar to thatshown in FIGURE 1.

Reference is made to the figures wherein like parts have likeidentifying numerals and, in particular to FIGURE 1 which illustrates aflow machine having a cylindrically bladed rotor 1 which is mounted, bymeans not shown, for rotation about its axis in the direction of thearrow 2. The rotor 1 has thereon blades 3 extending longitudinallythereof and having inner and outer edges 4 and 5 lying on inner andouter blade envelopes 6 and 7 formed when the rotor is rotated. Theblades 3 are concave facing the direction of rotation and have theirouter edges leading their inner edges.

First and second guide walls 8, 9 extend the length of the rotor 1between end walls 10 aligned with the ends of the rotor. The end walls10, only one of which is shown, cover the ends of the machine and may,although not necessarily, close the ends of the rotor. The walls 8 and 9define entry and exit regions S and P for flow of fluid to and from therotor. The guide wall 8 has an arcuate wall portion 11 on the exit sideof the rotor converging towards the rotor in the direction of rotationto form a converging gap or recess. A rounded auxiliary body 12extending parallel to the rotor axis between the end walls defines apassage 13 with the wall 11. The guide wall 8 has anoutlet wall portion14 defining with the guide wall 9 an exit duct 15, which, since itdiverges in the direction of flow, acts as a diffuser.

The wall 9 terminates at 16 which is spaced from the rotor a minimum ofone-half the blade depth and not more than three times the blade depthin order to minimize interference which causes an undesirable noise whenthe machine is operated, while at the same time providing a means toguide the flow leaving the machine. The zone 14 defines one end of boththe entry are and the exit arc. From the zone 16, the wall 9 divergessteadily from the rotor in the direction of rotation indicated by thearrow 2 with increasing radius of curvature; remote from the rotor thewall may be straight. The exit region P accordingly consists of achannel the median line of which is of spiral form.

It is preferred that not only the wall 9 but also the guide wall 8should be substantially spaced from the rotor; the machine can then bemade without adhering to close manufacturing tolerance, while stilleffectively separating the pressure and suction sides and maintainingthe relatively high efliciency of the machine. A machine constructedaccording to the invention and having such spacing lends itself readilyto sheet metal construction.

It will be noticed that the guide wall 8 subtends only a small angle atthe rotor axis, and since it presents a rounded nose 17 to the rotor itprovides negligible obstruction to air flowing in to or out from therotor. The auxiliary guide body 12 also does not obstruct such flow, asit too presents only a nose 18 to the rotor.

In operation of the FIGURE 1 machine, a vortex having a core whoseperiphery is defined by the stream line V and approximately a Rankinevortex is produced wherein the core is positioned eccentrically to therotor axis. The whole throughput of the machine flows twice through theblade envelope in a direction perpendicular to the rotor axis asindicated by the flow lines F, MF.

FIGURE 4 illustrates an ideal relation of the vortex to the rotor 1 andthe distribution of flow velocity in the vortex core and in the field ofthe vortex. The line 40 represents a part of the inner envelope 6 of therotor blades 3 projected onto a straight line while the line 41represents a radius of the rotor taken through the axis of the vortexcore. Velocity of fluid at points on the line 41 by reason of the vortexis indicated by the horizontal lines 43a, 43b, 43c and 43d, the lengthof these being the measure of the velocity at the points 43a 43b 43c and43d The envelope of these lines is shown by the curve 44 which has twoportions, portion 44a being approximately a rectangular hyperbola andthe other portion, 44b, being a straight line. Curve 44a relates to thefield region of the vortex and the curve 44b to the core. It will beunderstood that the curve shown in FIGURE 4 represents the velocity offluid where an ideal or mathematical vortex is formed, and that inactual practice, flow conditions will only approximate these curves.

The core of the vortex is a whirling mass of fluid with no translationalmovement as a whole and the velocity diminishes from the periphery ofthe core to the axis 42. The core of the vortex intersects the bladeenvelope as indicated at 40 and an isotach I within the vortex havingthe same velocity as the inner envelope contacts the envelope. Thevortex core is a region of low pressure and the location of the core ina machine constructed according to the invention can be determined bymeasurement of the pressure distribution within the rotor.

The velocity profile of the fluid where it leaves the rotor and passesthrough the path of the rotating blades will be that of the vortex. Inthe ideal case of FIGURE 4, this profile will be that of the Rankinevortex there shown by curves 44a and 44b, and in actual practice, theprofile will still be substantially that shown in FIGURE 4 so that therewill be around the periphery V of the core shown in FIGURE 1 a streamtube of high velocity whose centre line is the stream line MF, and thevelocity profile taken at the exit arc 13 will be similar to that shownin FIGURE 2 where the line FG represents the exit arc 13 and theordinates represent velocity. The curve shown exhibits a pronouncedmaximum point C which is much higher than the average velocityrepresented by the dotted line.

It will be appreciated that much the greater amount of fluid flows inthe flow tubes in the region of maximum velocity. It has been found thatapproximately 80% of the performance is concentrated in the portion ofthe output represented by the line AE which is less than 30% of thetotal are 13. A conventional velocity profile for fluid flow in adefined passage is illustrated by the way of contrast in FIGURE 3 wherethe average velocity of flow is represented by the dotted line. Thoseskilled in the art regard this profile as being approximately arectangular profile which following the principles generally adhered tois the sort of profile heretofore sought in the outlet of a flowmachine.

The maximum velocity C shown in FIGURE 2 appertains to the maximumvelocity stream tube. With a given construction the physical location ofthe flow tube MF may be closely defined. The relative velocity betweenthe blades and fluid in the restricted zone of the rotor blades 3through which the maximum velocity stream tube passes is much higherthan it would be if a flow machine were designed following theconditions adhered to heretofore in the art respecting the desirabilityof a rectangular velocity profile at the exit arc and even loading ofthe blades.

Under low Reynolds number conditions, this unevenness of the velocityprofile leads to beneficial results in that there will be lessseparation and energy loss in the restricted zone of the rotor bladesthrough which the high velocity stream tubes pass than if these streamtubes had the average velocity of throughput taken over the whole exitare 13 of the rotor. There is a more efficient transfer of momentum tothe fluid by the blades in this restricted zone and while the transferof momentum in the flow tubes travelling below the average velocity willbe less efiicient, nevertheless when all of the flow tubes areconsidered, there in a substantial gain in efficiency.

FIGURE 5 illustrates ideally a number of stream lines F characterizingstream tubes occurring within one half the rotor area defining by theinner envelope 6, it being understood that the stream tubes in the otherhalf of the rotor are similar. The centre line MP of the stream tubes ofhighest velocity is shown intersecting the envelope 6 at point 50 andthe isotach I as being circular when the whole rotor is considered. Itis seen that ideally the stream tubes of highest velocity undergo achange of direction of substantially 180 from the suction to thepressure sides when the flow in the whole rotor is considered. It isalso to be noted that the major part of the throughput, contained inthese stream tubes, passes through the rotor blades where the bladeshave a component of velocity in direction opposite to the main directionof flow Within the rotor indicated by the arrow A.

FIGURE 6 is a diagram showing the relative velocities of flow withrespect to a blade at the point 50 referred to in FIGURE 5. In thisfigure V represents the velocity of the inner edge of the blade 3 at thepoint 50, V the absolute velocity of the air in the flow tube MF at thepoint 50, and V the velocity of that air relative to the blade asdetermined by completing the triangle. The direction of the vector Vcoincides with that of the blade at its inner edge so that fluid flowsby the blade substantially without shock.

The character of a vortex is considered as being determined largely bythe blade angles and curvatures. The position of the vortex, on theother hand, is considered as being largely determined by theconfiguration of the vortex forming means which forms and stabilizes avortex in co-operation with the bladed rotor. The particular angles andcurvatures in any given case depend upon the following parameters: thediameter of the rotor, the depth of a blade in a radial direction, thedensity and viscosity of the fluid, the disposition of the vortexforming means and the rotational speed of the rotor, as well as theratio between overall pressure and back pressure. These parameters mustbe adapted to correspond to the operating conditions in a givensituation. Whether or not the angle and shape of the blades have beenfixed at optimum values is to be judged by the criterion that the streamtubes close to the vortex core are to be deflected approximately 180.

It is to be appreciated that the flow lines of FIGURE 1 do notcorrespond exactly to the position of the vortex core as illustrated inFIGURES 4 and 5 which represent the theoretical or mathematical flow.These latter figures show that it is desirable to have the axis of thecore of the vortex within the inner blade envelope 6 so that the isotachwithin the core is tangent to that envelope. Although this position isachieved in certain constructions hereinafter described, it is notessential, and in fact, is not achieved in the structure shown in FIGURE1.

It is further to be appreciated that despite the divergence of the flowin FIGURE 1 from the ideal, the stream tubes of highest velocity whichcarry a major part of the throughput are nevertheless turned through anangle of substantially 180 in passing from the suction to the pressureside of the rotor and that these stream tubes pass through the rotorblades where the blades have a velocity with a component opposite to themain direction of flow through the rotor as indicated by the arrow A.

It will be seen that peripheral flow tubes of the vortex core region Vflow through the passage 13 between the arcuate wall 11 defining theaforementioned recess and the auxiliary guide body 12.

The end wall 10 closing one end of the rotor has an aperture in theregion where the vortex core is formed. The aperture 155 has the shapeof a truncated sector which is adapted to be closed by a sector shapedcover plate 156 pivoted about an axis coinciding with the rotor axis.When the aperture 155 is completely opened, fluid enters through it fromthe exterior of the machine and spoils the vortex thus reducing thethroughput of the machine.

The machine shown in FIGURE 7 is similar in many respects to that ofFIGURE 1: the same references will be used for similar parts, which willnot require further description. In this machine a first guide wall 8 isshaped as a thin sector having its larger end rounded and having itsother end pivoted for movement about the axis 121. The vortex core isformed in the same manner as in FIGURE 1. When the wall 8 takes theposition shown in full line, the core takes the position shown. When thewall 8 is pivoted to the dotted position, the core is moved downwardly,thus changing the throughput of the machine.

The arrangement shown in FIGURE 7 also provides a means whereby adiffuser may be formed in one position of the wall 8 and where therewill be no diffuser effect when this wall is in another position. Thusthe wall 8 in the position shown in full lines diverges from a secondguide wall 9 in the direction of flow so that a diffuser is formed. Thewall 8 in the position shown in dotted lines, is substantially parallelto guide wall 9 so there is no dilluser effect at the outlet.

The throughput of a machine constructed according to the invention maybe further regulated, by means of a rod 123 which extends parallel tothe rotor along its length and is movable between the position shown infull lines and that shown in dotted.

We claim:

1. A cross flow fluid machine of the type comprising a hollow bladedcylindrical rotor mounted for rotation about its axis, a pair of endwalls substantially aligned with the ends of the rotor, the ends of therotor being substantially closed, first and second guide walls extendingbetween the end walls over the length of the rotor and definingtherewith an entry region and a discharge region said rotor and guidewalls co-operating on rotation of the rotor to set up and stabilize afluid vortex having a core region extending lengthwise of the axis andeccentric thereto adjacent the first guide wall and guiding a fluidthroughput through the rotor from the entry region through the path ofthe rotating blades of the rotor to the interior thereof and thenceagain through the path of the rotating blades to the discharge region,and a body in said discharge region extending parallel to the rotor axisbetween the end walls and spaced from the guide walls for flow of fluidto either side of said body.

2. A fluid machine as claimed in claim 1, wherein the body is of roundedform.

3. A fluid machine as claimed in claim 1, wherein the body lies close tothe first guide wall and defines therewith a passage for flow ofperipheral flow tubes of said vortex core region.

4. A fluid machine as claimed in claim 1, wherein the body is positionedwithin the discharge region between the periphery of the vortex coreregion and the adjacent flow tubes of the throughput.

5. A fluid machine of the type comprising a hollow bladed cylindricalrotor mounted for rotation about its axis, a pair of end wallssubstantially aligned with the ends of the rotor, the ends of the rotorbeing substantially closed, first and second guide walls extendingbetween the end walls over the length of the rotor and definingtherewith an entry region and a discharge region said rotor and guidewalls co-operating on rotation of the rotor set up and stabilize a fluidvortex having a core region extending lengthwise of the axis andeccentric thereto adjacent the first guide wall and guiding a fluidthroughput through the rotor from the entry region through the path ofthe rotating blades of the rotor to the interior thereof and thenceagain through the path of the rotating blades to the discharge region,the first guide wall subtending a small angle at the rotor axis andhaving adjacent the rotor an arcuate portion defining a recess, and arounded auxiliary guide body in said discharge region which is adjacentthe rotor spaced from the guide walls and extends parallel to the axisbetween the end walls, the guide body inducing flow tubes of the vortexcore region to circulate between said body and said recess with flowtubes of the throughput passing between the body and the second guidewall.

6. A fluid machine of the type comprising a hollow bladed cylindricalrotor mounted for rotation about its axis, a pair of end wallssubstantially aligned with the ends of the rotor, the ends of the rotorbeing substantially closed, first and second guide walls extendingbetween the end walls over the length of the rotor and definingtherewith an entry region and a discharge region said rotor and guidewalls co-operating on rotation of the rotor to set up and stabilize afluid vortex having a core region extending lengthwise of the axis andeccentric thereto adjacent the first guide wall and guiding a fluidthroughput through the rotor from the entry region through the path ofthe rotating blades of the rotor to the interior thereof and thenceagain through the path of the rotating blades to the discharge region,the first guide wall presenting an edge to the rotor in spaced relationthereto, and a rod-like body in said discharge region extending parallelto the rotor axis between the end walls and spaced between the guidewalls in a position adjacent and external to the vortex core region withflow tubes of said core region circulating between the body and thefirst guide wall and the throughput flow tubes passing between the bodyand said second guide wall.

References Cited UNITED STATES PATENTS 3,258,195 6/1966 Laing. 3,232,5222/1966 Laing.

FOREIGN PATENTS 876,620 9/1961 Great Britain.

HENRY F. RADUAZO, Primary Examiner.

US. Cl. X.R.

